X. Zhang, Y. Yan, and K. He, 
``Latency metric: an experimental method for measuring 
and evaluating parallel program and architecture scalability".  
Journal of Parallel and Distributed Computing, Vol. 22, No. 3, 1994.  


Latency measures the delay caused by communication between processors
and memory modules over the network in a parallel system.
Using intensive measurements and simulation, we show that
latency forms a major obstacle to improve parallel computing performance
and scalability. We present an experimental metric,
using network latency to measure and evaluate the
scalability of parallel programs and architectures.
This latency metric is an extension to the isoefficiency function 
and the isospeed metric.
We give a measurement method for using this latency metric, and
report the experimental results of evaluating the scalabilities of
several scientific computing
algorithms on the KSR-1 shared-memory architecture. Our analysis and
experiments show that the latency metric is a practical
method to effectively predict and evaluate scalability based on
measured latencies inherent in the program and the architecture.